This invention relates generally to the field of internal combustion engines, and more particularly to turbocharged internal combustion engines, and specifically to a method and apparatus for cooling a turbocharged locomotive engine.
Internal combustion engines such as the turbocharged diesel engines utilized for rail locomotives require cooling systems to limit the temperatures of various engine components. Such engines are designed with water jackets and/or internal cooling passages for the circulation of a water-based coolant to remove heat energy from the engine components such as the block and cylinder heads. Lubricating oil is circulated throughout the engine to reduce friction between moving parts and to remove heat from components such as the pistons and bearings. The lubricating oil must be cooled to maintain its lubricity and to extend the interval between oil changes. Some internal combustion engines utilize turbochargers to increase engine power output by compressing the intake combustion air to a higher density. Such compression results in the heating of the combustion air, which must then be cooled prior to entering the combustion chamber to enable the engine to have high volumetric efficiency and low emissions of exhaust pollutants. For mobile applications such as rail locomotives, it is known to use a pumped cooling medium such as water to transport heat to finned radiator tubes. The radiator tubes then transfer the heat to the ambient air, often using forced convection provided by a fan. One such system is described in U.S. Pat. No. 6,230,668 issued to Marsh, et al. and assigned to the assignee of the present invention. The cooling system described therein includes a two stage intercooler for conditioning the combustion air entering the engine. A first coolant loop includes a first stage intercooler and a second coolant loop includes a second stage intercooler. This two stage system provides an improved level of control for maintaining the engine, lubricating oil and combustion air temperatures within respective limits without excessive fan cycling.
The Environmental Protection Agency of the United States has established Tier 2 guidelines for emissions from locomotives utilizing a diesel engine as the prime mover power plant. The Tier 2 guidelines require a significant reduction in nitrous oxide (NOx) emissions from levels that are currently being achieved. A reduction in NOx generation can be achieved if the manifold air temperature (MAT) of the combustion intake air is maintained in a range of 110 to 125 degrees Fahrenheit. However, locomotives operate in extreme ambient temperature conditions (xe2x88x9240 to +120xc2x0 F.) and with transient power changes from 20 hp to 6250 hp in one minute. Tunnel operation may present ambient temperatures of up to 300xc2x0 F. for 20 minutes. Such operating conditions can cause turbocharger compressor outlet temperatures to approach 500xc2x0 F. As a result, modern locomotives utilizing exhaust gas driven turbocharged diesel engines currently operate with a MAT of between 145 to 220xc2x0 F.
Means for lowering manifold air temperature (MAT) have been incorporated in turbocharged piston engine powered vehicles for many decades. Lowering MAT can increase the power available from a given size engine and/or increase the durability of the engine at very high power loads by limiting the temperatures to which components, such as aluminum pistons, are exposed. For light weight vehicles such as piston powered military aircraft and racing automobiles, the need is usually for a large reduction in MAT for a short period of time. For such applications it has been feasible to carry a small amount of water which is injected into the hot intake air when needed. The injected water changes to steam due to the high temperature, thereby absorbing heat and lowering the intake charge temperature. For heavy mobile vehicles such as turbocharged diesel powered locomotives, which are designed to produce a maximum power output for an indefinite amount of time, it originally sufficed to use water based coolant circuits to transport the heat from an intercooler to a fan cooled radiator, with the coolant from the radiator used for both engine and intercooler alike. In order to cool MAT further and to produce more power from a given engine, U.S. Pat. No. 5,145,147 describes a split cooling system that produces colder water for the intercoolers than for the engine. U.S. Pat. No. 6,098,576 describes an enhanced split system that produces colder water for the oil cooler than for the engine.
Further reductions in NOx emissions are being required worldwide on prime movers such as ships, land vehicles, and stationary power plants. In the case of stationary power plants and ships utilizing diesel engines, it is still possible in many cases to meet reduced NOx limits with water based cooling systems that exchange heat to the environment using river, lake, or ocean water that rarely exceeds 80 F. However, this approach is not practical for a locomotive due to the need to haul the supply of water along with the train.
Accordingly, an improved cooling system and method of cooling a turbocharged land vehicle engine is needed.
An apparatus for conditioning a flow of combustion air being supplied to the intake of an internal combustion engine is described as including: an air-to-liquid heat exchanger disposed in the flow of combustion air for heat exchange between the combustion air and a liquid coolant; and an air-to-air heat exchanger disposed in the flow of combustion air downstream of the air-to-liquid heat exchanger for heat exchange between the combustion air and ambient air. The apparatus may include a flow control element for selectively bypassing at least a portion of the combustion air to the engine intake around the air-to-air heat exchanger. The apparatus may further include: a coolant circuit for delivering liquid coolant to the air-to-liquid heat exchanger; and wherein the coolant circuit comprises a control element for selecting the liquid coolant delivered to the air-to-liquid heat exchanger to be of a predetermined temperature relationship to that of the combustion air entering the air-to-liquid intercooler. The apparatus may include: a motor powered fan for moving ambient air through the air-to-air heat exchanger; and a flow path for supplying ambient air to the motor to ventilate the motor along a path other than that through the air-to-air heat exchanger.
A cooling system for an internal combustion engine is described as including: a liquid coolant circuit comprising an air-to-liquid intercooler for providing heat exchange between a liquid coolant and a flow of combustion air being supplied to an intake of an internal combustion engine; and an air-to-air intercooler disposed within the flow of combustion air downstream of the air-to-liquid intercooler for providing heat exchange between the flow of combustion air and ambient air. The liquid coolant circuit may further include at least one valve for controlling the liquid coolant delivered to the air-to-liquid intercooler to have a predetermined temperature relationship with the combustion air entering the air-to-liquid intercooler. The cooling system may further include: a fan motor disposed downstream of the air-to-air intercooler for driving a fan for forcing a flow of ambient air through the air-to-air intercooler; and a duct for supplying a flow of ambient air to ventilate the fan motor along a flow path other than that through the air-to-air intercooler.
A method of conditioning the combustion air being supplied to an internal combustion engine is described herein as including: directing compressed combustion air from a turbocharger to an air-to-liquid heat exchanger for heat exchange with a liquid coolant of an engine cooling system; and directing the compressed combustion air from the air-to-liquid heat exchanger to an air-to-air heat exchanger for heat exchange with ambient air. The method may include selectively bypassing the compressed combustion air around the air-to-air heat exchanger. The method may further include: forcing ambient air through the air-to-air heat exchanger with a suction fan driven by a suction fan motor; and providing cooling air to ventilate the suction fan motor along a flow path other than that through the air-to-air heat exchanger.
An internal combustion engine is described as including: an intake manifold for receiving combustion air into an engine; a coolant loop for circulating coolant for heat exchange between the engine and ambient air; an air-to-liquid intercooler having a combustion air side forming a first portion of a flow path of the combustion air to the intake manifold and having a liquid side forming a portion of the coolant loop for heat exchange between the combustion air and the coolant; and an air-to-air intercooler having a combustion air side forming a second portion of the flow path of the combustion air disposed downstream of the first portion and having an ambient air side for heat exchange between the combustion air and ambient air.